1. Field of the Invention
The present invention relates to a sample inclination measuring method for measuring an inclination of an axis of a columnar member such as a ferrule, for example, which is held by a clamping apparatus when analyzing the form or the like of a leading end part thereof by using a microscopic interferometer apparatus (also known as “interferometric microscope apparatus”), for example.
2. Description of the Prior Art
Research and development of optical fibers used for optical communications has recently been well underway.
Known as an example of this kind of optical fibers is one comprising a core having an outer diameter of about 10 μm; and a cladding layer, disposed at the outer periphery of the core, having an outer diameter of about 125 μm; while further comprising a ferrule, disposed at a connecting end part thereof, for connecting the optical fiber to another optical fiber.
The ferrule is a cylindrical component for holding and securing one end of the optical fiber in each of a set of plugs. After an optical fiber is inserted and secured with an adhesive or the like to the center part of the outer diameter of a ferrule, the leading end of the ferrule is polished into a mirror surface, so that two optical fibers held by respective ferrules can be connected to each other when the leading end faces of the two ferrules are butted against each other.
Conventionally known as the leading end face of the ferrule is one polished into a plane orthogonal to the optical axis.
For reducing the optical loss occurring when optical fibers are connected to each other, various high-precision specs on the order of μm have been defined by JIS Japanese Industrial Standard).
Also, there are cases where microscopic interferometer apparatus are used for inspecting whether produced ferrules conform to the specifications or not. A microscopic interferometer apparatus has been configured such that object light carrying phase information such as the surface form and refractive index distribution of a minute sample and reference light reflected from a predetermined reference plate are caused to interfere with each other, thus obtained interference fringes are observed, and forms and changes of the interference fringes are measured and analyzed, so as to attain the phase information of the sample.
When inspecting a produced ferrule by using such a microscopic interferometer apparatus, a clamping apparatus is disposed at a predetermined position in front of the reference plate, so as to hold the ferrule to be inspected.
Since the specification for the leading end face of the ferrule is on the order of μm as mentioned above, its measurement is required to be of a very high accuracy, which makes it difficult to attain a measurement accuracy suitable for the inspection even when the ferrule held by the clamping apparatus tilts only slightly. In some measurement items, a measurement accuracy suitable for the inspection is hard to attain unless the error in inclination between a normal of the reference surface of the microscopic interferometer apparatus and the axis of the ferrule is at an angle of 10 seconds or less.
Though the inclination of the clamping apparatus may be adjusted while the inclination of such a ferrule is directly measured, the measurement and adjustment therefor is quite complicated and requires a high accuracy, whereby errors in inclination cannot be adjusted easily.
In a ferrule of a type specified such that the inclination of the leading end face coincides with a perpendicular to the axis of the ferrule, the measurement can be made efficient if the angular error (perpendicularity) of the leading end face with respect to the perpendicular to the axis of the ferrule can be measured together with the inclination of the axis of the ferrule (concentricity).
For measuring the perpendicularity, a technique using an encoder to identify a predetermined angle (90°), and a technique directly determining the angle by using a level have also been tried. However, using such techniques is difficult to achieve highly accurate measurement results.